For centuries the boxwood was one of the most important garden trees. Hardly any other plant has influenced European garden culture as much as the box. The species has been suffering from shoot death for several years now. What does this mean and what helps?
What is boxwood shoot dieback and how can you combat it?
Box tree shoot dieback is a plant disease caused by the fungus Cylindrocladium buxicola and is manifested by symptoms such as orange to brown leaf spots, white spores on the underside of the leaves and balding shoots. Prevention and control include thinning, soil care and fungicide treatment.
What is boxwood shoot dieback?
Boxwood shoot dieback is a plant disease caused by the fungus Cylindrocladium buxicola. The fungus only affects boxwood plants, which include the common boxwood (Buxus sempervirens) and other species such as the small-leaved boxwood (Buxus microphylla) and ysander (Pachysandra). The disease has been known in England since the 1990s, but only appeared in Germany for the first time in 2004. It is also called “boxwood mushroom”.
What are the symptoms of boxwood shoot dieback?
Contrary to the name, shoot death affects not only the shoots, but also the leaves of the boxwood. You can recognize an infestation by these symptoms:
- initially individual orange to brown leaf spots
- colored darker at the edge
- get bigger over time and eventually merge
- white spores on the underside of the leaf
- black stripes on stems
- Shedding leaves, balding shoots
The fungal spores overwinter so that the boxwood becomes infected again every year. Infected plants are severely weakened and sooner or later die.
What causes boxwood shoots to die?
The death of shoots on the boxwood only occurs under certain weather conditions:
- high humidity (e.g. due to rain or humidity)
- Leaves must be permanently moist for at least five hours
- high temperatures around 25 degrees Celsius
At temperatures above 33 degrees Celsius and below five degrees Celsius, the fungus stops its activities. However, if the above conditions are met, the infection occurs within a few hours. The first symptoms appear after just a week. The fungal spores survive on shed leaves and can last up to four years.
Can you prevent boxwood shoots from dying?
In fact, shoot death in boxwood can be prevented with the following measures:
- plant insensitive boxwood varieties (e.g. Buxus microphylla)
- Particularly susceptible are 'Blauer Heinz' and 'Suffruticosa'
- plant in a windy and light location
- never water from above, always directly onto the ground
- Regularly thin out box trees that are too close together
- never cut when it rains
- preventive spraying with fungicides based on tebuconazole
But be careful: effective sprays may only be used in the garden under certain conditions. They are also harmful to many beneficial insects, e.g. E.g. parasitic wasps, ladybirds or predatory mites. This in turn could encourage further pest infestation.
What helps against shoot death in boxwood?
Unfortunately, only these measures help against shoot death on the boxwood:
- strong pruning of diseased plant parts
- Burn cuttings or dispose of them with household waste
- Do not compost clippings or leave them lying around!
- if necessary, transplant boxwood
- If necessary, replace the top layer of soil
Since the pathogen can survive in the soil, boxwood plants should no longer be planted in this area in the future to avoid reinfection. Furthermore, unfortunately only timely spraying helps.
Tip
What disease can the death of the instinct be confused with?
Shoot dieback can easily be confused with Volutella branch dieback. This is also a fungal disease, but is caused by a fungus of the species Volutella buxi.